Bowle in Germany....means punch. Generally, it relates to a good bit of alcohol, mixed into something.
If your German friend says "Feuerzangenbowle", then it's a traditional German drink which involves a rum-soaked sugarloaf....that is set on fire and drips down into a wine bowl. Generally, this is served around the holiday season. To be kinda honest, it's loaded with alcohol, and just two cups will get you going fairly quickly. If you consume six of these over a three hour period, you will be fairly drunk. So limit yourself to one or two max.
Another serious element of the bowle...is usually a lot of sugar added into the bowl. If a massive sugar rush bothers you.....skip the bowle no matter what it contains.
Generally, this bowle business will occur at a party or a neighbor's house when you've been invited over. The German passion for alcohol in the holiday season fits with it. Most of the times that you might run into this will be in the winter period, with heated bowle concoctions. There are summer types, but it's rare that you might run into this in July or August.